The technique of pulsed NMR is applied to the detailed study of molecular motions in a number of viscous liquids ((eta)(, )>(, )1 poise). Pressure studies are performed in order to examine explicitly the effect of volume on the motional characteristics. Where appropriate, ('13)C and ('2)D NMR are employed to obtain exclusively reorientational information, and to observe specific portions of the molecule. A prime concern of this work is to determine the validity range of the common hydrodynamic relationships at high viscosity. The overall objective of this work, then, is to provide a foundation for the systematic investigation of high viscosity fluid dynamics, as has been carried out for low viscosity liquids in this laboratory.A large portion of the work centers on cumene, since it is, perhaps, the simplest of high viscosity, non-associative liquids. A number of experiments have shown that cumene displays rather remarkable properties, which have been explained using models that coincidently are applied to glass transition phenomena. The actual motions are observed with NMR in order to determine the most accurate model predictions. To make such observations, it is necessary to unambiguously separate the translational from the rotational contributions to the NMR relaxation. Thus, this work reports the first isotopic dilution study of a selectively deuterated liquid of this type.Dimethyl phthalate (DMP) has a number of properties resembling those of cumene. However, the actual temperature of the analogous effects is somewhat higher for DMP, thus enabling a full pressure study to be performed. Once again, this was done as a function of isotopic dilution.The results of this work point to the presence of high frequency rotational motions, even at high viscosity where translational motion is significantly slowed. This high frequency motion quickly dominates the T(,1) process. The T(,1(rho)), however, remains sensitive to the slower, more weakly distributed translational motions, which appear to follow the Stokes-Einstein equation, as shown in the DEHP study.